The invention relates to the field of optical wave guides and more particularly to a voltage-induced optical waveguide modulator.
It is known to provide optical switching and modulating devices utilizing the properties of electrooptic crystals. As disclosed in an article by D. J. Channin entitled "Voltage-Induced Optical Waveguide", Applied Physics Letters, Vol. 19, No. 5, Sept. 1, 1971 at page 128, and in U.S. Pat. No. 3,795,433 entitled "Voltage-Induced Optical Waveguide Means" issued Mar. 5, 1974 to R.C.A Corporation, a voltage-induced optical waveguide may be constructed by depositing two parallel electrodes on the optically-polished surface of lithium niobate (LiNbO.sub.3). A voltage differential applied to the electrodes produces a high electric field concentration in the crystal directly below the gap separating the electrodes. An optical waveguide is formed in the localized region of modified refractive index produced by the electric field through the electro-optic effect. Various means may be used for applying and extracting light energy to the waveguide region. By varying the voltage across the electrodes, the device can function as an optical switch or analog modulator.
Previous such voltage-induced optical waveguide devices have utilized, as described in the Channin article, a gap separating the electrodes of approximately seventy microns. It was thought that such a gap was necessary to avoid sparking between the electrodes. The problem with such a configuration is that a high turn-on voltage is required due to the distance between the electrodes, and there is increased uncertainty in the location of the output light spot or two separate output light spots may be created. Also, the optical throughput of the prior devices tends to be lower than optimal due to scattering of the light by the electrodes.